A well typically includes a borehole (or “wellbore”) that is drilled into the earth to provide access to a geological formation below the earth's surface (or “subsurface formation”). A portion of a subsurface formation that contains (or is at least expected to contain) mineral deposits is often referred to as a “reservoir”. A reservoir that contains hydrocarbons, such as oil and gas, is often referred to as a “hydrocarbon reservoir”. A well can facilitate the extraction of natural resources, such as hydrocarbons, from a subsurface formation, facilitate the injection of fluids into the subsurface formation, and facilitate the evaluation and monitoring of the subsurface formation. In the petroleum industry, wells are often drilled to extract (or “produce”) hydrocarbons, such as oil and gas, from hydrocarbon reservoirs located in subsurface formations. The term “oil well” is often used to describe a well designed to produce oil. In the case of an oil well, some natural gas is typically produced along with oil. Wells producing both oil and natural gas are sometimes referred to as “oil and gas wells” or “oil wells.” The term “gas well” is normally reserved to describe a well designed to produce primarily natural gas. The term “hydrocarbon well” is often used to describe both oil and gas wells.
Creating a hydrocarbon well typically involves several stages, including drilling, completion and production. The drilling stage normally includes drilling a wellbore into a hydrocarbon reservoir in an effort to access hydrocarbons trapped in the reservoir. The drilling process is often facilitated by a drilling rig that sits at the earth's surface. The drilling rig provides for operating a drill bit; hoisting, lowering and turning drill pipe and tools; circulating drilling fluids; and generally controlling operations in the wellbore (or “downhole”). Drilling fluid (or “drilling mud”) is typically circulated into the wellbore during drilling operations to provide hydrostatic pressure to prevent formation fluids from flowing into the wellbore, to cool and clean the drill bit, and to carry drill cuttings away from the drill bit and out of the wellbore. For example, drilling fluid is pumped down into the wellbore to circulate around the drill bit, capture drill cuttings created by the drill bit cutting into the formation rock, and carry the drill cuttings to the surface. The “dirty” drilling fluid is often filtered to remove drill cuttings and other debris from the drilling fluid to “clean” the drilling fluid so that it can be recirculated through the wellbore or otherwise reused. Referring again to the stage of creating a well, the completion stage typically involves making the well ready to produce hydrocarbons. In some instances, the completion stage includes lining portions of the wellbore and pumping fluids into the well to fracture, clean or otherwise prepare the reservoir to produce hydrocarbons. The production stage typically involves extracting and capturing (or “producing”) hydrocarbons from the reservoir via the well. During the production stage, the drilling rig is normally removed and replaced with a collection of valves (or a “production tree”), that regulates pressure in the wellbore, controls production flow from the wellbore, and provides access to the wellbore. A lifting device, such as a pump jack, can provide hydrostatic lift that assists in drawing the hydrocarbons to the surface from the reservoir, especially in instances where the pressure in the well is so low that the hydrocarbons do not flow freely up the wellbore, to the surface. Flow from an outlet valve of the production tree is normally coupled to a distribution network, such as pipelines, storage tanks, and transport vehicles that transport the production to refineries and export terminals.
When developing a well it can be useful to know characteristics of the subsurface formation. Subsurface formation characteristics can, for example, be used for drilling operation planning and execution, hydraulic fracturing operation planning and execution, and wellbore stability planning and execution. Characteristics of interest can include mechanical properties, such as the fracture toughness of the subsurface formation. Fracture toughness defines the ability of a material, such as the rock of the subsurface formation, to resist fracture propagation when a crack is present. Fracture toughness can be used, for example, in hydraulic fracturing operation planning and execution to determine a pressure required to fracture the rock of the subsurface formation to facilitate the flow of hydrocarbons through the formation and into a well. Fracture toughness is also a critical material characteristic used in simulating lost circulation materials (LCM) management. LCM are often added to drilling fluids over the course of drilling to prevent loss of fluid to fractures in the formation, or provided as needed to seal fractures or zones in which significant losses have already occurred. Fracture toughness values can be of paramount importance in managing LCM and stabilizing a well due to lost mud and fracture gradient overshooting. Thus, fracture toughness logging information can enable optimization of drilling to prevent drilling mud losses. Traditional well assessment techniques, such as downhole logging operations, and core sampling operations are routinely employed to estimate the mechanical properties of subsurface formations.